Demodulator having automatic quadrature control function

ABSTRACT

A demodulator for automatically performing quadrature control in which there is no necessity for the modulator side to perform precision adjustment and deterioration in characteristics e.g., error rate is suppressed for long. The demodulator includes a quadrature controller fed with an in-phase component and a quadrature component output from the quadrature detecting unit to correct quadrature error between phases of in-phase and quadrature signals based on a quadrature error signal, an automatic gain controller AGC outputting in-phase and quadrature components of a demodulated signal corrected for amplitude errors by an amplitude error signal, an error detection unit fed with in-phase and quadrature components of the demodulated signal to output in-phase and quadrature components and polarity signals, an amplitude error detector outputting in-phase and quadrature components of the amplitude error to the AGC based on the in-phase and quadrature components and the respective polarity signals, and a quadrature error detection unit generating a quadrature error signal Qd based on the in-phase and quadrature components and the polarity signals to output the generated quadrature error signal to the quadrature controller.

FIELD OF THE INVENTION

This invention relates to a demodulator and, more particularly, to ademodulator for automatically correcting errors in a detection signal ofa quadrature detected modulated signal in a digital radio communicationsystem.

BACKGROUND OF THE INVENTION

FIG. 11 shows a typical structure of a conventional demodulator.Referring to FIG. 11, this demodulator includes a quadrature detectingunit 1, an automatic amplitude controller (AGC) 3, an error detectionunit 3 and an amplitude error detection unit 4.

An input modulated signal is assumed to have been modulated inaccordance with a quadrature modulation system, such as QPSK (quadraturephase shift keying) or QAM (quadrature amplitude modulation). Therespective quadrature components (channels) are termed an in-phasecomponent or channel (Ich) and a quadrature component or channel (Qch),respectively. A quadrature detecting unit 1 receives a quadraturemodulated signal, as an IF (intermediate frequency) signal, and outputsan output signal as baseband signals Ich1 and Ich2. Meanwhile, thequadrature detecting unit 1 is made up of a known detection circuit,such as a synchronous detector, a semi-synchronous detector, or a delaydetector.

The AGC 2 is fed with Ich2 and Qch2 and, using amplitude error signalsAi, Aq, fed from the amplitude error detection unit 4, corrects theamplitude errors to output signals Ich3, Qch3 each having a regularamplitude.

The error detection unit 3 uses (receives) Ich3, Qch3, output from theAGC 2, to output error signals Ei, Eq and polarity signals Di, Dq.

The amplitude error detection unit 4 uses the signals Ei, Eq, Di and Dq,output by the error detection unit 3, to output Ai and Aq as respectiveamplitude error signals of Ich and Qch.

SUMMARY OF THE DISCLOSURE

However, there is much to be desired in the art and various problemshave been encountered in the course of the investigations toward thepresent invention. That is, it is not possible with the conventionaldemodulator shown in FIG. 11 to correct quadrature deviation produced inmodulation.

Recently, an analog IC devices, termed quadrature modulators, aremanufactured and marketed, such that there is now commercially availablesuch a device automatically performing quadrature adjustment of themodulator. However, this device cannot be said to be of high precision.In particular, the device cannot be said to cope with multi-valuemodulation system, such as QAM, such that, if this device is put topractical use, the BER (bit error rate) tends to be lowered. Ultimately,the quadrature deviation in a modulator in the multi-valued modulationsystem has to be adjusted mainly by manual operations.

As described above, it is not possible in the conventional demodulatorsto correct the quadrature deviation produced at the time of modulation.

It was necessary to make manual analog adjustment except if an analogquadrature modulator can be applied. So, a quadrature adjustment processwas required during device production etc., thus necessitating redundanttime and operating steps.

Moreover, the demodulation circuit, adjusted manually in an analogfashion, is liable to degradation due to temperature or humidity of theanalog components, while being liable to deterioration with lapse oftime, resulting in that quadrature properties cannot be maintained forprolonged time.

Thus, if quadrature errors are produced on the modulator side,correction is not possible with the conventional demodulator so thatdemodulated signals (playback signals) such as shown in FIG. 8 areproduced, thus naturally deteriorating the characteristics such as errorrate.

In view of the above-described status of the art, it is an object of thepresent invention to provide a demodulator which, by performingautomatic correction of quadrature errors in a digital fashion.

It is another object of the present invention, to provide a demodulatorwhich renders it unnecessary to make precision adjustment on themodulator side and which assures operational stability and highreliability without producing deterioration in characteristics such aserror rate for a prolonged time.

Further objects of the present invention will become apparent in theentire disclosure.

According to an aspect of the present invention there is provided ademodulator which comprises;

-   -   a quadrature controller for correcting quadrature errors of a        signal quadrature-detected by a quadrature detecting unit, and a        quadrature error detection unit for detecting a quadrature error        based on an error signal detected as to in-phase and quadrature        components from a demodulated signal output from an automatic        gain controller fed with an input signal corrected for        quadrature errors as an output signal of the quadrature        controller, to feed the detected quadrature error (signal) to        the quadrature controller.

According to a second aspect of the present invention, there is provideda demodulator which comprises;

-   (a) a quadrature detecting unit fed with and quadrature-detecting a    quadrature modulated signal to output an in-phase component and a    quadrature component;-   (b) a quadrature controller fed with the in-phase component and the    quadrature component output from the quadrature detecting unit, the    quadrature controller correcting a quadrature error between the    in-phase component and the quadrature component based on an input    quadrature error signal, and outputting the resulting signal;-   (c) an automatic gain controller fed with the in-phase component and    the quadrature component output from the quadrature controller and    outputting signals corrected for amplitude errors based on the input    amplitude error signal as the in-phase component and the quadrature    component of a demodulated signal;-   (d) an error detection unit detecting, from the in-phase component    and the quadrature component of the demodulated signal output from    the automatic gain controller, an in-phase component of the error    signal and a polarity signal of the in-phase component of the    demodulated signal, and a quadrature component of the error signal    and a polarity signal of the quadrature component of the demodulated    signal;-   (e) an amplitude error detection unit generating an in-phase    component and a quadrature component of an amplitude error signal    based on the in-phase component of the error signal output from the    error detection unit and the polarity signal of the in-phase    component of the demodulated signal, and on the quadrature component    of the error signal and the polarity signal of the quadrature    component of the demodulated signal, to output the generated    in-phase and quadrature components of the amplitude error signal to    the automatic gain controller; and-   (f) a quadrature error detect ion unit generating a quadrature error    signal based on the in-phase component of the error signal and the    polarity signal of the in-phase component of the demodulated signal,    both output from the error detection unit, and on the in-phase    component of the error signal and the polarity signal of the    quadrature component of the demodulated signal to feed the generated    quadrature error signal to the quadrature controller.

According to a third aspect of the present invention there is provided ademodulator which comprises;

-   (a) a quadrature detecting unit fed with a quadrature modulated    signal as an input signal to quadrature-detect the input signal to    output in-phase and quadrature components of a regular amplitude;-   (b) a quadrature controller fed with the in-phase and quadrature    components output from the quadrature detection unit to correct the    quadrature error between phases of the in-phase and quadrature    components, based on a quadrature error signal;-   (c) an automatic gain controller fed with the in-phase and    quadrature components output from the quadrature controller to    output signals corrected for respective amplitude errors as in-phase    and quadrature components of a demodulated signal;-   (d) an error detection unit detecting an in-phase component of an    error signal and a polarity signal of the in-phase component of the    demodulated signal, and a quadrature component of the error signal    and a polarity signal of the quadrature component of the demodulated    signal, from the in-phase and quadrature components of the    demodulated signal output from the automatic gain controller; and-   (e) a quadrature error detection unit generating a quadrature error    signal based on the in-phase component of the error signal and the    polarity signal of the in-phase component of the demodulated signal,    and the quadrature component of the error signal and a polarity    signal of the quadrature component of the demodulated signal, all    output from the error detection unit, to feed the generated    quadrature error signal to the quadrature controller.

Further aspects of the present invention are disclosed in the claims,particularly in the dependent claims.

In a fourth aspect, the quadrature controller comprises;

-   -   a first low-pass filter fed with the quadrature error signal        output from the quadrature error detection unit to smooth out        and output the quadrature error signal;    -   a first multiplier multiplying the quadrature component output        from the quadrature detecting unit with an output of the first        low-pass filter; and    -   a first adder adding the in-phase component output from the        quadrature detecting unit and an output of the first multiplier;    -   the quadrature component output from the quadrature detecting        unit being directly output, an output of the first adder being        output as an in-phase component corrected for quadrature errors.

In a fifth aspect, the quadrature error detection unit comprises;

-   -   a second multiplier multiplying the in-phase component of the        error signal (Ei) output from the quadrature detecting unit with        the polarity signal (Dq) of the quadrature component of the        demodulated signal;    -   a third multiplier multiplying the quadrature component of the        error signal (Eq) output from the quadrature detecting unit with        the polarity signal (Di) of the in-phase component of the        demodulated signal; and    -   a second adder summing outputs of the second and third        multipliers;    -   an output signal of the second adder being output as the        quadrature error signal (Qd).

In a sixth aspect, the automatic gain controller comprises;

-   -   a second low-pass filter smoothing out and outputting the        in-phase component of the amplitude error signal output from the        amplitude error detection unit;    -   a third low-pass filter smoothing out and outputting the        quadrature component of the amplitude error signal output from        the amplitude error detection unit;    -   a fourth multiplier multiplying the in-phase component output        from the quadrature controller as an input signal with an        in-phase component of the amplitude error signal smoothed out by        the second low-pass filter, the fourth multiplier outputting the        result of multiplication as the in-phase component of the        demodulated signal; and    -   a fifth multiplier multiplying the quadrature component output        from the quadrature controller as an input signal with a        quadrature component of the amplitude error signal smoothed out        by the third low-pass filter, the fifth multiplier outputting        the result of multiplication as the quadrature component of the        demodulated signal.

In a seventh aspect, the automatic gain controller comprises;

-   -   a first absolute value computing circuit determining an absolute        value of the in-phase component output from the quadrature        controller;    -   a second absolute value computing circuit determining an        absolute value of the quadrature component output from the        quadrature controller;    -   a third adder adding together outputs from the first and second        absolute value computing circuit;    -   a fourth low pass filter smoothing out an output of the third        adder;    -   a sixth multiplier multiplying an in-phase component output from        the quadrature controller with an output of the fourth low pass        filter; and    -   wherein the quadrature component output from the quadrature        controller is directly output as the quadrature component, and        an output of the sixth multiplier is output as the in-phase        component of the demodulated signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of an embodiment of the present invention.

FIG. 2 shows a structure of an AGC according to an embodiment of thepresent invention.

FIG. 3 shows a structure of an LPF according to an embodiment of thepresent invention.

FIG. 4 shows a structure of an error detection unit according to anembodiment of the present invention.

FIG. 5 shows a structure of an amplitude error detection unit accordingto an embodiment of the present invention.

FIG. 6 shows a structure of quadrature error detection unit according toan embodiment of the present invention.

FIG. 7 shows a structure of quadrature controller according to anembodiment of the present invention.

FIG. 8 is a graph showing demodulated signals on occurrence ofquadrature deviation in QPSK modulation on an I-Q complex plane.

FIG. 9 shows a modified embodiment of the present invention.

FIG. 10 shows a structure of an AGC according to the modified embodimentof the present invention.

FIG. 11 shows a structure of a conventional demodulator.

PREFERRED EMBODIMENTS OF THE INVENTION

A preferred embodiment of the present invention is now explained.Referring to FIG. 1, a preferred embodiment of the demodulator of thepresent invention includes a quadrature detecting unit 1, a quadraturecontroller 6, and an automatic amplitude controller (AGC) 2 in thisorder of signal flow, and further a feed back circuitry comprising anerror detection unit 3, an amplitude error detection unit 4 andquadrature error detection unit 5. The quadrature detecting unit 1 isfed as an input signal with an intermediate frequency (IF IN) signal forquadrature-detecting the input signal to output an in-phase componentIch1 and a quadrature component Qch1. The quadrature controller 6 is fedwith an in-phase component and a quadrature component output from thequadrature detecting unit 1 to correct the quadrature error based onquadrature error signal Qd. The automatic gain controller AGC 2 is fedwith the in-phase and quadrature components Ich2, Qch2 output from thequadrature controller 6 to output signals, which are corrected forrespective amplitude errors by in-phase and quadrature components Ai, Aqof the amplitude error, as in phase and quadrature components Ich3, Qch3of the demodulated signal. The error detection unit 3 is fed with thein-phase and quadrature components Ich2, Qch3 of the demodulated signaloutput from the automatic gain controller 2, and detects and outputs anin-phase component and a polarity signal Ei, Di of the error signal anda quadrature component and a polarity signal Eq, Dq of the error signal.The amplitude error detection unit 4 outputs an in-phase component and aquadrature component Ai, Aq of the amplitude error to the automatic gaincontroller 2 based on a polarity signal Di of the in-phase componentIch3 of the demodulated signal and the in-phase component Ei of theerror signal, and on a polarity signal Dq of the quadrature componentQch3 of the demodulated signal and the quadrature component Eq of theerror signal, Di, Dq, Ei and Eq being output by the error detection unit3. The quadrature error detection unit 5 generates a quadrature errorsignal Qd based on an in-phase component Ei and a polarity signal Di ofthe error signal and a quadrature component Eq and polarity signal Dq ofthe error signal, Ei, Di, Eq and Dq being output from the errordetection unit 3, and outputs the quadrature error signal Qd to thequadrature controller 6. The quadrature error between phases of thein-phase component Ich and the quadrature component Qch generated at thetime of modulation is corrected by the quadrature controller 6.

Referring to FIG. 7, the quadrature controller 6 includes a firstlow-pass filter 63 for smoothing the quadrature error signal Qd outputfrom the quadrature error detection unit, a first multiplier 62 formultiplying the quadrature component Qch1 output from the quadraturedetecting unit with an output of the first low-pass filter 63, and afirst adder 61 for adding the in-phase component Ich1 output from thequadrature detecting unit and an output of the first multiplier 62. Thequadrature component output from the quadrature detecting unit isdirectly output as Qch2, an output of the first adder 61 being output asan in-phase component Ich2 corrected for quadrature errors.

Referring to FIG. 6, the quadrature error detection unit 5 includes asecond multiplier 51 for multiplying an in-phase component of an errorsignal (Ei) output from the error detection unit 3 with a polaritysignal Dq of a quadrature component Qch3 of the demodulated signal, athird multiplier 52 for multiplying a quadrature component Eq of theerror signal output from the error detecting unit 3 with a polaritysignal Di of the in-phase component Ich3 of the demodulated signal, anda second adder 53 for summing outputs of the second and third adders 51,52, wherein an output of the second adder 53 is output as a quadratureerror signal (Qd).

Referring to FIG. 2, the automatic gain controller 2 includes a secondlow-pass filter 24 for smoothing out an in-phase component Ai of anamplitude error signal output from the amplitude error detection unit 4;a third low-pass filter 23 for smoothing out a quadrature component Aqof the amplitude error signal output from the amplitude error detectionunit 4; a fourth multiplier 21 for multiplying the in-phase componentIch2 output from the quadrature controller 6 with an in-phase componentAi of the amplitude error signal smoothed out by the second low-passfilter 24 for outputting the result of multiplication as an in-phasecomponent Ich3 of the demodulated signal; and a fifth multiplier 22 formultiplying the quadrature component Qch2 output from the quadraturecontroller 6 with a quadrature component Aq of the amplitude errorsignal smoothed out by the third low-pass filter 23 for outputting theresult of multiplication as a demodulated quadrature signal Qch3.

In a preferred embodiment, shown in FIG. 9, the demodulator of thepresent invention includes quadrature detecting unit 7 fed as an inputsignal with an intermediate frequency signal IF IN forquadrature-detecting the input signal to output an in-phase componentIch1 and a quadrature component Qch1; a quadrature controller 6 fed withthe in-phase and quadrature components output from the quadraturedetecting unit 1 to correct the quadrature error based on quadratureerror signal Qd; an automatic gain controller 8 fed with the in-phaseand quadrature components Ich2, Qch2 output from the quadraturecontroller 6 to output signals corrected for respective amplitude errorsas in-phase and quadrature components Ich3, Qch3 of a demodulatedsignal; an error detection unit 3 fed with the in-phase and quadraturecomponents of the demodulated signal output from the automatic gaincontroller 8 to detect and output an in-phase component and its polaritysignal (Ei, Di) of the error signal and a quadrature component and itspolarity signal (Eq, Dq) of the error signal; and a quadrature errordetection unit 5 for generating a quadrature error signal Qd based on anin-phase component Ei and its polarity signal Di of the error signaloutput from the error detect ion unit 3 and on a quadrature component Eqand its polarity signal Dq of the error signal to output the quadratureerror signal Qd to the quadrature controller 6.

Referring to FIG. 10, the automatic gain controller 8 includes a firstabsolute value computing circuit 82 for determining an absolute value ofan in-phase component output from the quadrature controller; a secondabsolute value computing circuit 83 for calculating an absolute value ofa quadrature component Qch2 output from the quadrature controller 6; anadder 84 for summing an output value of the second absolute valuecomputing circuit 83 with an output value of the first absolute valuecomputing circuit 82; a fourth low-pass filter 85 for smoothing anoutput of the adder 84; and a sixth multiplier 81 for multiplying thein-phase component Ich2 output from the quadrature controller with anoutput of the fourth low-pass filter 85. An output Qch2 of quadraturecontroller 6 is output directly as a quadrature component Qch3 of thedemodulated signal, while an output of the sixth multiplier 81 is outputas an in-phase component Ich3 of the demodulated signal.

[Preferred Embodiments]

For further explaining the preferred embodiments of the presentinvention, an example of the present invention is explained withreference to the drawings.

FIG. 1 shows a configuration of an embodiment of a demodulator of thepresent invention. Referring to FIG. 1, an embodiment of the presentinvention includes a quadrature detecting unit 1, an AGC 2, an errordetection unit 3, an amplitude error detection unit 4, a quadratureerror detection unit 5, and a quadrature controller 6. It is assumedthat the input modulation signal has been modulated in accordance withthe quadrature modulation system, such as QPSK or QAM. For each of thequadrature components (channels), appellations of in-phase component(channel, Ich) and quadrature component (channel, Qch) are used.

The quadrature-detecting unit 1 demodulates input quadrature modulatedsignals, as IF (intermediate frequency) signals, into baseband signalsIch1 and Qch1. Meanwhile, the quadrature-detecting unit 1 is made up ofknown detection circuits, such as a synchronous detection circuit, a sub(or quasi)-synchronous circuit and/or a delay detection circuit.

The quadrature controller 6 is fed with baseband signals Ich1, Qch1,output by the quadrature detecting unit 1, to output signals Ich2, Qch2,freed of quadrature errors, using a quadrature error signal Qd inputfrom the quadrature error detection unit 5.

The AGC 2 is fed with Ich2, Qch2 to output Ich3, Qch3, having regular(or normal) amplitudes, using amplitude error signals Ai, Aq input fromthe amplitude error detection unit 4.

The error detection unit 3 outputs error signals Ei, Eq and polaritysignals Di, Dq, using Ich3, Qch3, output from the AGC 2.

The amplitude error detection unit 4 outputs amplitude error signals Ai,Aq of Ich and Qch, respectively, using the outputs Ei, Eq, Di, Dq outputby the error detection unit 3.

The quadrature error detection unit 5 outputs the quadrature errorsignal Qd, using the outputs Ei, Eq, Di, Dq supplied from the errordetection unit 3.

Referring to the drawings, the structure of respective elements of thedemodulator are hereinafter explained.

FIG. 2 shows an illustrative structure of the AGC 2. Referring to FIG.2, the AGC 2 is made up of multipliers 21, 22 and low-pass filters(LPFs) 23, 24. The AGC 2 performs amplitude control so that the signalsIch2, Qch2 output by the quadrature controller 6 will be at regularsignal point positions, using the amplitude error signals Ai, Aq, outputby the amplitude error detection unit 4, to produce modulated signalsIch3, Qch3.

FIG. 3 shows an illustrative structure of the LPFs 23, 24 of the AGC 2and an LPF 63 contained in the quadrature controller 6. Referring toFIG. 3, the LPF is comprised of an integrator made up of a flip-flop 232operating as a delay element and an adder 231. That is, the currentsignal and a signal delayed by one clock by the flip-flop 23 are summedtogether by the adder 231 and latched and output by the flip-flop 232.

FIG. 4 shows an illustrative structure of the error detection unit 3.Referring to FIG. 4, the error detection unit 1 is made up of signalpoint error detection units 31, 32. The signal point error detectionunits 31, 32 detect errors (deviations) from the regular signal pointpositions of the input signals Ich3, Qch3 to output error (deviation)signals Ei Eq.

If the input signals Ich3, Qch3 are deviated in the positive or negativedirection from the regular signal point positions, the output errorsignals Ei, Eq assume negative and positive values, respectively. Sincethe regular signal point positions vary with modulation systems used, asignal MOD specifying the modulation system is supplied to the signalpoint error detection units 31, 32. The polarity signals Di, Dqrepresent polarities of the signal Ich3, Qch3, respectively, and areacquired from respective sign bits.

FIG. 5 shows the structure of the amplitude error detection unit 4.Referring to FIG. 5, the amplitude error detection unit 4 includes amultiplier 42 for multiplying the in-phase component Ei of the errorsignal and its polarity signal Di to output the amplitude error signalAi, and a multiplier 41 for multiplying the quadrature component Eq ofthe error signal and its polarity signal Dq to output an amplitude errorsignal Aq.

FIG. 6 shows the structure of the quadrature error detection unit 5.Referring to FIG. 6, the quadrature error detection unit 5 is made up ofmultipliers 51, 52 and an adder 53. The results of multiplication of Eiwith Dq and those of Eq with Di in the multipliers 51, 52 are summedtogether in the adder 53 to give a quadrature error signal Qd (see thefollowing equation (1)).

FIG. 7 shows the structure of the quadrature controller 6. Referring toFIG. 7, the quadrature controller 6 is made up of an adder 61, amultiplier 62 and a low pass filter LPF 63.

The quadrature error signal Qd, output from the quadrature errordetection unit 5, is smoothed by the LPF 63, an output of which ismultiplied by the multiplier 62 with Qch1. The resulting product issummed (added) in the adder 61 with Ich1 (Ich1 less the product obtainedon multiplication) and the resulting sum is output as Ich2 to correctthe quadrature error. The output Qch2 on the Qch side is no other thanQch1.

The operation of an example of the present invention is explained mainlywith reference to the quadrature controller 6.

The signal point error signals Ei, Eq, obtained by the error detectionunit 3, and the polarity signals Di, Dq, indicate whether the reproducedsignal is deviated from the regular signal point position in thepositive direction or in the negative direction. For quadrature control,these signals need to be converted into quadrature error (deviation)signals.

FIG. 8 shows on an I-Q complex plane the modulated signal in case ofoccurrence of a quadrature deviation. It is seen from FIG. 8 that, sincethe distances between respective signal points and the point of originare inherently equal to each other, the signal points should bepositioned on apex points of a square. However, these signal points areactually positioned on apex points of a diamond shape. In order tocorrect this state, such error signals, which will correct the deviationin the diagonal directions from the regular signal points, as shown inFIG. 8, are required.

For obtaining these error signals, it is only sufficient if thequadrature error signals Qd, represented by the following equation (1):Qd=Ei·Dq+Eq·Di  (1)

-   -   is used.

The quadrature error detection unit 5 generates this Qd.

The quadrature error control based on quadrature error signals isexplained. Assume that the IF input signal to a quadrature detectionunit 7 is A (t), an angular velocity of a local oscillator, not shown,in the quadrature detection unit 7, is ω rad/sec and a quadrature erroris δ rad, the signals Ich, Qch input to an A/D (analog/digital)converter, not shown, supplying Ich1, Qch1 of digital signals to thequadrature controller 6, are given by the following equations (2) and(3):Ich=A(t)cos(ωt+δ)=A(t)cos ωt·cos δ−A(t) sin ωt·sin δ=A(t)cos ωt·cosδ−Qch·sin δ  (2)Qch=A(t)sin ωt  (3).

For demodulating this signal regularly, δ in Ich of the above equation(2) needs to be eliminated. However, the term of A(t)cos ωt·cos δrepresents merely a lowered gain of Ich and can be corrected by AGC2.

So, in the Ich of the above equation (2), it suffices if the term of−Qch·sin δ in Ich of the equation (2) is corrected.

Since δ may be regarded as a constant for a short period of time, theproduct of the quadrature error signal with the Qch value may be summed(added) to Ich to correct the quadrature error. In an embodiment of thepresent invention, the above-mentioned correction operation is performedin the quadrature controller 6 shown in FIG. 7.

A further embodiment of the present invention is now explained. FIG. 9shows a second embodiment of the present invention. Referring to FIG. 9,the second embodiment of the present invention differs from the firstembodiment shown in FIG. 1 as to the quadrature detecting unit 7 and theAGC 8.

In the above-described first embodiment, in which the AGC 2 corrects theamplitudes of Ich and Qch, it is unnecessary for thequadrature-detecting unit 1 to output a signal of the regular amplitude.On the other hand, in the second embodiment of the present invention,the quadrature detecting unit 7 outputs signals of the regularamplitude. So, it is unnecessary for the AGC 8 to perform the operationfor causing the output signal to be on the regular amplitude, such thatit is only necessary for the AGC 8 to correct the lowering of the gainof Ich that is not corrected by the quadrature controller 6.

FIG. 10 shows an illustrative structure of the AGC 8. Referring to FIG.11, the AGC 8 is made up of a (sixth) multiplier 81, absolute valuecircuits (calculating units) 82, 83, an adder 84 and an (fourth) LPF 85.The absolute value circuits 82, 83 determine the amplitudes of Ich2 andQch2 and a relative magnitude (difference) thereof by the adder 84 toobtain an amplitude error signal between Ich and Qch. It is noted thatthe adder 84 operates as a subtractor for outputting a difference valuecorresponding to the output value of the absolute value circuit 83 lessthe output value of the absolute value circuit 82. The amplitude errorsignal obtained by the adder 84 is smoothed by the LPF 85. The smoothedamplitude error signal is multiplied by the Ich by the multiplier 81.The resulting product is output as Ich3. The Qch2 from the quadraturecontroller 6 is directly output as Qch3 to correct the ampitudedifference between Ich and Qch.

The meritorious effects of the present invention are summarized asfollows.

The present invention provides a configuration comprising a quadraturecontroller correcting quadrature errors of a signal quadrature-detectedby a quadrature detecting unit, and a quadrature error detecting unitdetecting a quadrature error, wherein the quadrature errors arecorrected based on an error signal detected as to in-phase andquadrature components of a demodulated signal output from an automaticgain controller fed as an input signal with an output signal of thequadrature controller, and the detected quadrature error Qd is fed tothe quadrature controller. Therefore, it is unnecessary to make manualadjustment of analog circuit elements such that quadrature errors of themodulator can be eliminated fully digitally and automatically. Moreover,the present invention gives a meritorious effects that full digitizationfacilitates designing as LSI.

It should be noted that other objects, features and aspects of thepresent invention will become apparent in the entire disclosure and thatmodifications may be done without departing the gist and scope of thepresent invention as disclosed herein and claimed as appended herewith.

Also it should be noted that any combination of the disclosed and/orclaimed elements, matters and/or items might fall under themodifications aforementioned.

1. A demodulator comprising: (a) a quadrature controller fed with asignal quadrature-detected by a quadrature detecting unit as an inputsignal to correct a quadrature error between phases of an in-phasecomponent and a quadrature component of said signal based on aquadrature error signal used for correcting said quadrature error tooutput a corrected signal; (b) an error detection unit detecting anerror signal between the in-phase component and the quadrature componentof a demodulated signal output by an automatic gain controller fed withan output signal of said quadrature controller corrected for quadratureerror; and (c) a quadrature error detection unit detecting thequadrature error based on said error signal to feed the quadrature errorsignal to said quadrature controller.
 2. A demodulator comprising: (a) aquadrature detecting unit fed with and quadrature-detecting a quadraturemodulated signal to output an in-phase component and a quadraturecomponent; (b) a quadrature controller fed with the in-phase componentand the quadrature component output from said quadrature detecting unit,said quadrature controller correcting the quadrature error between thein-phase component and the quadrature component based on an inputquadrature error signal, and outputting the resulting signal; (c) anautomatic gain controller fed with the in-phase component and thequadrature component output from said quadrature controller andoutputting signals corrected for amplitude errors based on the inputamplitude error signal as the in-phase component and the quadraturecomponent of a demodulated signal; (d) an error detection unitdetecting, from the in-phase component and the quadrature component ofthe demodulated signal output from said automatic gain controller, anin-phase component of said error signal and a polarity signal of thein-phase component of the demodulated signal, and a quadrature componentof the error signal and a polarity signal of the quadrature component ofsaid demodulated signal; (e) an amplitude error detection unitgenerating an in-phase component and a quadrature component of anamplitude error signal based on the in-phase component of said errorsignal output from said error detection unit and the polarity signal ofthe in-phase component of the demodulated signal, and on the quadraturecomponent of the error signal and the polarity signal of the quadraturecomponent of said demodulated signal, to output the generated in-phaseand quadrature components of said amplitude error signal to saidautomatic gain controller; and (f) a quadrature error detection unitgenerating a quadrature error signal based on the in-phase component ofthe error signal and the polarity signal of the in-phase component ofsaid demodulated signal, both output from said error detection unit, andon the in-phase component of said error signal and the polarity signalof the quadrature component of said demodulated signal to feed thegenerated quadrature error signal to said quadrature controller.
 3. Ademodulator comprising: (a) an quadrature detecting unit fed with aquadrature modulated signal as an input signal to quadrature-detect theinput signal to output in-phase and quadrature components of a regularamplitude; (b) a quadrature controller fed with the in-phase andquadrature components output from the quadrature detection unit tocorrect the quadrature error between phases of the in-phase andquadrature components, based a quadrature error signal; (c) an automaticgain controller fed with the in-phase and quadrature components outputfrom said quadrature controller to output signals corrected forrespective amplitude errors as in-phase and quadrature components of ademodulated signal; (d) an error detection unit detecting an in-phasecomponent of an error signal and a polarity signal of the in-phasecomponent of the demodulated signal, and a quadrature component of theerror signal and a polarity signal of the quadrature component of thedemodulated signal, from the in-phase and quadrature components of thedemodulated signal output from the automatic gain controller; and (e) aquadrature error detection unit generating a quadrature error signalbased on the in-phase component of the error signal and the polaritysignal of the in-phase component of the demodulated signal, and thequadrature component of the error signal and a polarity signal of thequadrature component of the demodulated signal, all output from saiderror detection unit, to feed the generated quadrature error signal tosaid quadrature controller.
 4. The demodulator as defined in claim 2wherein said quadrature controller comprises: a first low-pass filterfed with said quadrature error signal output from said quadrature errordetection unit to smooth out and output said quadrature error signal; afirst multiplier multiplying the quadrature component output from saidquadrature detecting unit with an output of said first low-pass filter;and a first adder adding the in-phase component output from saidquadrature detecting unit and an output of said first multiplier; thequadrature component output from said quadrature detecting unit beingdirectly output, an output of said first adder being output as anin-phase component corrected for quadrature errors.
 5. The demodulatoras defined in claim 3 wherein said quadrature controller comprises: afirst low-pass filter fed with said quadrature error signal output fromsaid quadrature error detection unit to smooth out and output saidquadrature error signal; a first multiplier multiplying the quadraturecomponent output from said quadrature detecting unit with an output ofsaid first low-pass filter; and a first adder adding the in-phasecomponent output from said quadrature detecting unit and an output ofsaid first multiplier; the quadrature component output from saidquadrature detecting unit being directly output, an output of said firstadder being output as an in-phase component corrected for quadratureerrors.
 6. A demodulator comprising: (a) a quadrature detecting unit fedwith and quadrature-detecting a quadrature modulated signal to output anin-phase component and a quadrature component; (b) a quadraturecontroller fed with the in-phase component and the quadrature componentoutput from said quadrature detecting unit, said quadrature controllercorrecting the quadrature error between the in-phase component and thequadrature component based on an input quadrature error signal, andoutputting the resulting signal; (c) an automatic gain controller fedwith the in-phase component and the quadrature component output fromsaid quadrature controller and outputting signals corrected foramplitude errors based on the input amplitude error signal as thein-phase component and the quadrature component of a demodulated signal;(d) an error detection unit detecting, from the in-phase component andthe quadrature component of the demodulated signal output from saidautomatic gain controller, an in-phase component of said error signaland a polarity signal of the in-phase component of the demodulatedsignal, and a quadrature component of the error signal and a polaritysignal of the quadrature component of said demodulated signal; (e) anamplitude error detection unit generating an in-phase component and aquadrature component of an amplitude error signal based on the in-phasecomponent of said error signal output from said error detection unit andthe polarity signal of the in-phase component of the demodulated signal,and on the quadrature component of the error signal and the polaritysignal of the quadrature component of said demodulated signal, to outputthe generated in-phase and quadrature components of said amplitude errorsignal to said automatic gain controller; and (f) a quadrature errordetection unit generating a quadrature error signal based on thein-phase component of the error signal and the polarity signal of thein-phase component of said demodulated signal, both output from saiderror detection unit, and on the in-phase component of said error signaland the polarity signal of the quadrature component of said demodulatedsignal to feed the generated quadrature error signal to said quadraturecontroller, wherein said quadrature error detection unit comprises: afirst multiplier multiplying the in-phase component of the error signal(Ei) output from said quadrature detecting unit with the polarity signal(Dq) of the quadrature component of said demodulated signal; a secondmultiplier multiplying the quadrature component of the error signal (Eq)output from said quadrature detecting unit with the polarity signal (Di)of the in-phase component of said demodulated signal; and an addersumming outputs of said first and second multipliers; an output signalof said adder being output as said quadrature error signal (Qd).
 7. Ademodulator comprising: (a) an quadrature detecting unit fed with aquadrature modulated signal as an input signal to quadrature-detect theinput signal to output in-phase and quadrature components of a regularamplitude; (b) a quadrature controller fed with the in-phase andquadrature components output from the quadrature detection unit tocorrect the quadrature error between phases of the in-phase andquadrature components, based a quadrature error signal; (c) an automaticgain controller fed with the in-phase and quadrature components outputfrom said quadrature controller to output signals corrected forrespective amplitude errors as in-phase and quadrature components of ademodulated signal; (d) an error detection unit detecting an in-phasecomponent of an error signal and a polarity signal of the in-phasecomponent of the demodulated signal, and a quadrature component of theerror signal and a polarity signal of the quadrature component of thedemodulated signal, from the in-phase and quadrature components of thedemodulated signal output from the automatic gain controller; and (e) aquadrature error detection unit generating a quadrature error signalbased on the in-phase component of the error signal and the polaritysignal of the in-phase component of the demodulated signal and thequadrature component of the error signal and a polarity signal of thequadrature component of the demodulated signal, all output from saiderror detection unit, to feed the generated quadrature error signal tosaid quadrature controller, wherein said quadrature error detection unitcomprises: a first multiplier multiplying the in-phase component of theerror signal (Ei) output from said quadrature detecting unit with thepolarity signal (Dq) of the quadrature component of said demodulatedsignal; a third multiplier multiplying the quadrature component of theerror signal (Eq) output from said quadrature detecting unit with thepolarity signal (Di) of the in-phase component of said demodulatedsignal; and an adder summing outputs of said first and secondmultipliers, an output signal of said adder being output as saidquadrature error signal (Qd).
 8. The demodulator as defined in claim 2wherein said automatic gain controller comprises: a first low-passfilter smoothing out and outputting the in-phase component of theamplitude error signal output from said amplitude error detection unit;a second low-pass filter smoothing out and outputting the quadraturecomponent of the amplitude error signal output from said amplitude errordetection unit; a first multiplier multiplying the in-phase componentoutput from said quadrature controller as an input signal with anin-phase component of the amplitude error signal smoothed out by saidfirst low-pass filter, said first multiplier outputting the result ofmultiplication as the in-phase component of the demodulated signal; anda second multiplier multiplying the quadrature component output fromsaid quadrature controller as an input signal with a quadraturecomponent of the amplitude error signal smoothed out by said secondlow-pass filter, said second multiplier outputting the result ofmultiplication as the quadrature component of the demodulated signal. 9.A demodulator comprising: (a) an quadrature detecting unit fed with aquadrature modulated signal as an input signal to quadrature-detect theinput signal to output in-phase and quadrature components of a regularamplitude; (b) a quadrature controller fed with the in-phase andquadrature components output from the quadrature detection unit tocorrect the quadrature error between phases of the in-phase andquadrature components, based a quadrature error signal; (c) an automaticgain controller fed with the in-phase and quadrature components outputfrom said quadrature controller to output signals corrected forrespective amplitude errors as in-phase and quadrature components of ademodulated signal; (d) an error detection unit detecting an in-phasecomponent of an error signal and a polarity signal of the in-phasecomponent of the demodulated signal, and a quadrature component of theerror signal and a polarity signal of the quadrature component of thedemodulated signal, from the in-phase and quadrature components of thedemodulated signal output from the automatic gain controller; and (e) aquadrature error detection unit generating a quadrature error signalbased on the in-phase component of the error signal and the polaritysignal of the in-phase component of the demodulated signal, and thequadrature component of the error signal and a polarity signal of thequadrature component of the demodulated signal, all output from saiderror detection unit to feed the generated quadrature error signal tosaid quadrature controller, wherein said automatic gain controllercomprises: a first absolute value computing circuit determining anabsolute value of the in-phase component output from said quadraturecontroller; a second absolute value computing circuit determining anabsolute value of the quadrature component output from said quadraturecontroller; a third adder adding together outputs from the first andsecond absolute value computing circuits; a fourth low pass filtersmoothing out an output of the third adder; a sixth multipliermultiplying an in-phase component output from said quadrature controllerwith an output of the fourth low pass filter; and wherein the quadraturecomponent output from the quadrature controller is directly output asthe quadrature component, and an output of the sixth multiplier isoutput as the in-phase component of the demodulated signal.